Claus was very well educated and inclined to literature but eventually took up a military career. In 1926, he joined the Reiter- und Kavallieregiment 17. Adolf Hitler came to power in 1933, and while some aspects of the party were repugnant to him, Stauffenberg was not initially in complete opposition to their ideas. This changed after the Kristallnacht in November 1938. The systematic maltreatment of the Jews, and suppression of religion in Germany, made him more and more and more an opponent of the Nazis.
On 1 January 1937 he was promoted to the rank of Hauptmann (captain), a rank he would hold for the next six years. His regiment was involved in the occupation of the Sudetenland and, once war broke out, in the Polish, French and Russian campaigns. In 1940 he was awarded the iron Cross First Class.
Promoted to Oberstleutnant (lieutenant colonel), on 1 January 1943, he was afterwards transferred to the North African campaign. While scouting out a new command area, his vehicle was strafed by marauding British fighter-bombers and he was severely wounded. He was taken back to Germany by plane and spent three months in hospital.
His right hand had been removed at the wrist in the war hospital in North Africa, he had also lost the first and third finger on his left hand. A splinter of metal had to be removed from one knee and his left eye was gone. After recuperating from his wounds, he was posted as a staff officer to the Replacement Army located in an office in Bendlerstrasse in Berlin. In this office Claus became involved in a plot to kill Adolf Hitler. The attempt was to take place at the military high command Wolfsschanze near Rastenburg, East Prussia.
Claus von Stuaffenberg had gone to a meeting attended by Hitler and left a briefcase, packed with explosives and a ten to fifteen minute timer, under the table announced he had to make an urgent call and quickly left the room. However, the brief case was slightly moved and four people were killed and almost all present were injured, Hitler was injured only lightly as he was shielded from the blast by a heavy, solid oaken conference table. Adolf Hitler, via the radio on 20 July 1944, announced the failure of the attempt.
Stauffenberg and his aide de camp, Leutnant Werner von Haefte, had quickly walked away and flown back to Berlin, where he learned about the failure. Stauffenberg was captured and, with other officers, later shot that night by firing squad in the courtyard of the Bendlerblock in Berlin.
Another central figure in the plot was Stauffenberg's eldest brother, Berthold, who was tried in the People's Court by Roland Freisler on 10 August. Berthold was one of eight conspirators executed by strangulation, hanged slowly in Plötzensee Prison, Berlin, later that day.
The widowed Nina Stauffenberg and their children were also arrested by the SS. Nina was kept behind to give birth to her last child but the others were sent to prison camps. Once her baby was born, Nina was able to elude the SS and with her baby went to relatives. The other children were expected to change their names to Meister and were moved from prison to prison. In the final hours of the Second World War they were about to be executed when the SS decided not to carry out the order when they became aware that British troops were within 400 meters of their location.